Method for the treatment of scale

ABSTRACT

METHOD FOR THE TREATMENT OF SCALE, PARTICULARLY CALCIUM SULFATE SCALE, USING A WATER SOLUBLE PARTIALLY ESTERIFIED POLYPHOSPHORIC ACID HAVING A PRESCRIBED FORMULA, THE CORRESPONDING WATER SOLUBLE SALTS AND MIXTURES.

United States Patent 3,806,451 METHOD FOR THE TREATMENT OF SCALE Jack F.Tate, Houston, Tex., assignor to Texaco Inc., New York, N.

No Drawing. Continuation-impart of application Ser. No. 887,312, Dec.22, 1969. This application Sept. 22, 1971, Ser. No. 182,880

Int. Cl. C02b 5/02, 5/04, 5/06 US. Cl. 21058 3 Claims ABSTRACT OF THEDISCLOSURE Method for the treatment of scale, particularly calciumsulfate scale, using a water soluble partially esterified polyphosphoricacid having a prescribed formula, the corresponding water soluble saltsand mixtures.

This application is a continuation-in-part application of my applicationSer. No. 887,312, filed Dec. 22, 1969, now abandoned.

This invention is directed to a method useful in the prevention and/orinhibition of the build-up of undesirable inorganic mineral scaledeposits in oil and gas wells, their flow lines, auxiliary producingequipment, such as heat exchangers and cooling towers, as well as theproducing strata in the vicinity of the well bore. More particularly,the invention is useful in the prevention and/or inhibition of build-upof scale deposits on a surface contacted by water containing scaleforming quanities of sulfates such as calcium or barium.

The term surface as used in the accompanying specification and claimsincludes the metal surfaces of equipment used in gas and oil wells, theflow lines, and auxiliary producing equipment; the water storage tanks,and the like, heat exchangers, evaporative coolers and so forth, as wellas the surfaces of producing strata in and around the well bore and inthe formation, that come in contact with water containing scale formingconstituents.

The formation of objectionable scale deposits, such as calcium or bariumsulfate is rather widespread in certain production areas, and has beenattributed to several causes. One generally accepted theory of scaleformation is that of chemical precipitation resulting from thecommingling of two fluid streams each of which contains a concentrationof a particular ion such that when they commingle an unstable water isproduced. For example, in the case of calcium sulfate scale formation,one stream contains sulfate ions, and the other calcium ions in suchconcentration so as to produce an unstable water. The mixing of thesestreams at the well bore may result in the deposition of a hardcrystalline calcium sulfate deposit which gradually builds up on thewalls of the well tubing, for example, to a point where it may choke offfluid flow in the tube if remedial measures were not undertaken.

Another cause of the scale formation is attributed to the precipitationof scale material from potentially supersaturated solutions thereof.When the operating variables of temperature and pressure changeadversely, or solvent is allowed to evaporate, thus concentrating thesolution precipitation of the salt in the tubing and surrounding strataoccurs.

The use of strong alkali solutions for the removal of sulfate scale hasbeen proposed. It has been claimed that under certain favorableconditions of temperatures and time, concentrated alkali solutions will,in some cases, provide a break-up of the built-up scale after relativelylong periods of treatment. If, for example, a calcium sulfate scale istreated with concentrated potassium hydroxide for comparatively longperiods of time, say from 24 to 72 hours, it has been claimed that awhite flufi'y pre- "Ice cipitate of calcium hydroxide will be formed.This precipitate may then be removed by suitable mechanical means. Sucha method is obviously undesirable in that considerable periods of timeare involved and the use of mechanical apparatus is expensive, and insome cases, either undesirable or mechanically impossible. Moreover,strong alkali is not effective in preventing or inhibiting the build-upof scale deposits in well tubing, producing equipment and the producingstrata about the bore hole.

It is accordingly an object of this invention to provide a method ofinhibiting and/ or preventing the build-up of scale deposits in gas andoil flow lines, auxiliary equipment, well tubing and the surroundingsubsurface strata.

A further object is to provide a scale treating method for use inpreventing the build-up of scale deposits in the well tubing, producingequipment, the bore hole and surrounding strata.

A still further object of this invention is to provide a method for thetreatment of gas and oil well tubing and the like containing sulfatescale therein to prevent and/ or inhibit the build-up of further scaledeposits in the tubing.

These as well as other objects are accomplished according to the presentinvention which comprises a scale prevention and/or inhibitioncomposition comprising an aqueous solution of a water soluble partiallyesterified polyphosphoric acid compound having the general formulawherein A represents a hydrogen atom or an alkali metal, R represents analkyl group containing from 1 to 10 carbon atoms therein, and n is aWhOle number from 2 to 6, and mixtures thereof, said treatingcomposition having an average apparent molecular weight in the range offrom about 206 to about 1300, preferably from about 380 to about 700,being employed in an amount sufiicient to inhibit the development ofscale in an aqueous system.

The invention also comprises a method of treating equipment susceptibleto the development of scale deposits therein such as water storage tanksand the like, particularly oil field equipment, using the scaleprevention composition.

Representative phosphate ester compounds within the scope of thisinvention include the preferred compounds, tetraethyltetraphosphoricacid, tetrapropyltetraphosphoric acid, tripentyltriphosphoric acid, andtrihexyltriphosphoric acid, and broadly encompass compounds such asdimethyldiphosphoric acid, hexamethylhexaphosphoric acid,tri(decyl)triphosphoric acid, hexa(decyl)hexaphosphoric acid, thecorresponding alkali metal salts and mixtures thereof.

The aforesaid esters can be prepared by known preparative methods suchas by dehydration of phosphoric acid and partial esterification with asuitable alkanol or mixed alkanols, optionally followed byneutralization with alkali metal salt solutions or by partialesterification of phosphoric acid, followed by dehydration andoptionally neutralization is part of one or all of the acidic hydrogenatoms.

In carrying out one aspect of the present invention the method thereofcomprises introducing the scale prevention composition into theequipment to be protected, such as oil well tubing, in the form of anaqueous solution in an amount sufficient to provide the phosphate estercompound therein at a concentration of from about 0.001 to about 0.30%by weight and maintaining the scale treating composition in contact withthe internal surfaces thereof for a contact time sufficient to preventand/ or inhibit the development of scale depositions or additional scaledeposits therein. It is desirable to circulate the scale preventioncomposition through the system to provide adequate contact of thecomposition with the surfaces to be protected. Underground stratasurrounding the well bore can be treated in a like mannner, i.e. bypassing the solution into said strata such as by injection of thesolution down through the bore hole or production tubing, preferablyunder pressure.

In general it has been found that excellent protection againstobjectionable scale deposits can be obtained by maintaining the treatingcomposition in contact with the scale for a contacting time period offrom about 2 to about 24 hours and preferably between about 4 to 12hours. This contacting time period can also be advantageously used inareas containing some scale deposits such as oil field tubing to preventor inhibit the build-up of additional scale deposits therein. In areaswhere heavy scale deposits are present or are likely to be encountered,the contacting time period can be extended to 24 hours or more withoutany harmful effects. If treatment is carried out at fairly frequentintervals with the composition of the present invention, i.e. on asemiweekly or weekly basis, then shorter contacting times (e.g.averaging about 4 to -12 hours) can be used. Less frequent treatingintervals, i.e. at about every 10 or days generally necessitatecorresponding longer contacting times that may average between 12 and 24hours.

The scale prevention composition is used in an amount sufiicient toprovide to the treating solution the phosphate ester compound in anamount of from 0.001 to about 0.30% by weight. It has been found thatexcellent results are obtained with the phosphate ester compound atconcentrations in the range of from about 0.001 to 0.10% by weight.Higher concentraitons (above about 0.03%) do not provide improved scaleprotection.

A more complete understanding of the invention will be obtainable fromthe following illustrative examples.

The following procedure was used in the evaluations.

A 1000 milliliter glass beaker was provided with suificient calciumsulfate and sodium chloride, obtained by mixing solutions of calciumchloride and sodium sulfate, to produce an aqueous concentration thereofof 10,000 p.p.'m. of calcium sulfate and 50,000 p.p.m. of sodiumchloride. A preweighed metal rotor attached to an externally providedmechanical stirring device was immersed in the test solution for a 24hour time period. The test solution containing a predetermined quantityof the test material was maintained at a temperature of 104 F. duringthe test period. At the end of the 24 hours, the rotor was removed fromthe test solution and from the stirrer. The scale deposited on the rotorwas removed, dried and weighed. In all, several tests were conducted oneach material being evaluated and the average of the tests was taken asthe amount of scale deposit formed during the test period. The abovelaboratory test procedure affords good correlation between the resultsthereby obtained and larger scale field evaluations of scale preventingcompositions. In addition a control test was run under the sameconditions except that no test material was added to the test solution.

The following table records the results of the test.

1 Control is a blank example, i.e., the test procedure was run withoutany phosphate compound present in the test solution.

B Additive A is dipotassium tetra(alkyl)tetraphosphate wherein eachalkyl group contains three carbon atoms.

From the data presented in the above table, it is evident taht thephosphate ester compounds of the present invention are eifective calciumsulfate scale inhibitors at low concentrations.

Obviously, other modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. Method of controlling the build-up of calcium and barium sulfatescale on a surface contacted with water containing said scale-formingconstituents by incorporating in said water an aqueous solutionconsisting of from about 0.01 to about 0.30% by weight of a memberselected from the group consisting of tetrapropyltetraphospohric acid,the corresponding alkali metal salts and mixtures thereof, said memberbeing maintained in contact with said surface for a period of from about2 to about 24 hours to prevent the build-up of scale thereon.

2. Method as claimed in claim 1 wherein said member is present in anamount of from about 0.001 to 0.01% by weight.

3. Method as claimed in claim 1 wherein said salt is dipotassiumtetra-propyltetraphosphate.

References Cited UNITED STATES PATENTS 3,429,824 2/1969 Tate 2523,168,554 2/1965 Phillips et a1 260'933 X 2,947,774 8/1960 Levine260-933 X 3,462,365 8/1969 Vogelsang 252-180 X 3,510,436 5/1970Silverstein et a1. 2l-2.7 A

HARRY WONG, JR., Primary Examiner US. Cl. X.R.

(5/69) UNITED STATES PATENT OFFICE V CERTIFICATE OF CORRECTION PatentNo. D d April 23, 97

Inventor( Jack F. Tate It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected vas shown below:

I'C'ol. 2, line 60 J "is" should read --in-- line 68 'O.30%" should read--0.03%-- col. 3, line 30 "0.30%" should read --o.o3%-- line 32 "0.10%"should read ---0.0l% line 32 "concentraitons" should read--concentrations-- Col. t, line 17 "taht" should read -tha.t--

line 30 "0.30%" should read --0.03%-- line 32 "pohric" should read--phoric-- Signed and sealed this 10th day of September I 97L|..

(SEAL) Attest: I

' MCCOY M. GIBSON, JR. C MARSHALL DANN Attest ing Officer 7 Commissionerof Patents UNITED STATES PATENT OFFICE 7 CERTIFICATE OF CORRECTIONPatent No. D t d April 23, 197

Inventor(s) Jack F. Tate It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

01. 2 line 60 "is" should read --in-- j m line 68 "0.30%" should read"0.03%."

Y '1. line 30 "0.30%" should read "0.03%" 00 3, line 32 "0.10%" shouldread "0.01%"

I line 32 "concentraitons" should read --concentrations-- 4 line 17"taht" should read -that-- CO1 line 30 "0.30%" should read --0.03%--line 32 "pohric" should read --phoric-- Signed and sealed this 10th dayof September 197L (SEAL) Attest:

MCCOY M. GIBSON, JR. 0 MARSI IALL DANN Attesting Officer Commissloner ofPatents

